a) Field of the Invention
This invention relates to a webbing retractor for use in a seat belt system of an automotive vehicle or the like, and more specifically to an improvement in a webbing retractor of the type that, when tensile force of at least a predetermined value is applied to a webbing due to an impact of a collision, the webbing is allowed to extend out to more effectively protect the body of an occupant.
b) Description of the Related Art
It has been the practice to use a webbing retractor, for example, in an automotive vehicle or the like to wind up a webbing which serves to restrain the body of an occupant in a seat in the event of an emergency such as a collision.
Such webbing retractors include those designed in such a way that, when a tensile force applied to the webbing by an impact is smaller than a predetermined value, the body of the occupant is restrained in the seat by simply preventing further release of the webbing but that, when tensile force applied to the webbing is greater than the predetermined value, the energy of the tensile force applied to the webbing is absorbed while allowing the webbing to extend out, whereby an abrupt deceleration or acceleration of the body of the occupant upon a collision is lessened to better protect the body of the occupant.
As a webbing retractor operating in this way, Japanese Patent Publication (Kokoku) No. SHO 57-21347, for example, discloses a webbing retractor of the type that, when a spindle and a bobbin undergo relative rotation, a flange is caused to move in a threaded fashion from a side of the spindle toward a side of the bobbin and an energy-absorbing member arranged there-between is hence caused to collapse to absorb energy.
Further, Japanese Utility Model Application Laid-Open (Kokai) No. HEI 1-145760 discloses a webbing retractor of the type that, when force of at least a predetermined value is applied, a spindle and a bobbin undergo relative rotation and a coil spring secured at one end thereof to the spindle and at an opposite end thereof to the bobbin is hence twisted to absorb energy.
To lessen an abrupt deceleration which acts upon the body of an occupant in the event of a collision, the greater the length of a webbing to be extended upon application of tensile force of at least a predetermined value to the webbing, the better. However, an unduly large extended length results in the potential danger that the body of the occupant may be allowed to move forward too much and may hit the steering wheel, the instrument panel and/or the like.
Further, to lessen the abrupt deceleration which acts upon the body of the occupant in the event of the collision, it is necessary not only to allow the webbing to simply extend out but also to sufficiently absorb the energy of tensile force applied to the webbing.
Because of the use of threaded members, the webbing retractor disclosed in Japanese Patent Publication (Kokoku) No. SHO 57-21347 referred to above is however accompanied by the drawback that to make the energy-absorbing member collapse for the absorption of sufficient energy, the bobbin has to be rotated a few times and the webbing is allowed to extend too much during that time.
On the other hand, the webbing retractor disclosed in Japanese Utility Model Application Laid-Open (Kokai) No. HEI 1-145760 referred to above is accompanied by the drawback that the extendible length of the webbing cannot be controlled because it is uncertain how long the relative rotation between the bobbin and the spindle would last.